The invention relates to a hydraulic circuit for controlling a system comprised of a clutch and a brake with separate clutch and brake in the main drive of a mechanical press, wherein clutch and brake are movable by a piston/cylinder unit between the coupling position and the braking position and wherein the piston/cylinder unit can be connected communicatingly to the pressure line by a press safety valve for torque generation at the clutch and wherein the brake is spring-loaded against the engagement direction of the clutch.
Such systems comprised of a clutch and a brake either have individual clutches and individual brakes or they are known in the form of a clutch/brake combination. For this reason, the clutch/brake combinations dealt with in the following also encompass all systems acting in the same way and being comprised of a clutch and a brake, since the invention is suitable for both embodiments.
Such hydraulic circuits serve for connecting mechanical presses either to a drive or for holding them by means of a brake in a standstill position, wherein the mechanical presses are used, for example, for producing carbody parts.
Since in this connection masses weighing tons are to be accelerated or to be a decelerated, the applicable safety standards require that in the case of power outage the braking function must cause standstill, if possible, within the range of a few hundredth of a second, while, on the other hand, correspondingly rapid engagement times for the clutch are to be realized when the press operation is to be started up again.
This requirement is to be viewed in connection with the transfer of the workpieces into the press so that very short stop times or acceleration times are desired.
However, these time periods cannot become arbitrarily short because this would lead to very high accelerations acting on the clutch and the brake and, as a result of this, on the entire drive strand of the machine so that the drive would be exposed to unacceptably high stress loads.